Lubricant Composition

ABSTRACT

A lubricant composition, which comprises a fluoro-oil, a powdery fluororesin thickener, and Ca salt or Na salt of aromatic sulfonic acid or saturated aliphatic dicarboxylic acid as a rust-inhibitive additive, where the thickener is in a proportion of 10-40% by weight, and the additive is in a proportion of 0.3-10% by weight, on the basis of total weight of the composition, the balance being the fluoro-oil. The lubricant composition containing the powdery fluororesin in an appropriate admixing proportion as a thickener in the fluoro oil has a distinguished rust inhibition, particularly even after having being subjected to heat hysteresis, where a perfluoropolyether oil is usually used as a fluoro-oil.

TECHNICAL FIELD

The present invention relates to a lubricant composition, and more particularly to a lubricant composition with a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis.

BACKGROUND ART

Lubricants such as grease, etc. are widely used in lubrication of various machines including automobiles, construction machines, industrial machines, machine tools, etc., and also various parts as members of the machines. The machines have a possibility of water intrusion, depending on the locations where they are used, and thus requirements for the rust inhibition thereof are more and more strict. Furthermore, recent trends towards higher speed, much more size reduction, higher performance, lighter weight, etc. have made service temperatures of these peripheral equipment higher and higher, so the rust inhibition after having been subjected to such heat hysteresis has been also an important requirement.

To improve the rust inhibition use of some of additives have been studied. A grease composition for ball-and-roller bearings, which comprises a grease composition containing silicone oil- or fluorocarbon oil-based lubricating oil as a base oil, and a rust inhibitor comprising a magnesium compound and a volatile rust inhibitor as essential components has been so far proposed, where triazole-based compound such as benzotriazole, methylbenzotriazole, etc., or dicyclohexyl ammonium nitrite have been recommended as preferable volatile rust inhibitors.

Patent Literature 1: JP-A-9-59664

The proposed grease composition for ball-and-roller bearings is said to have a distinguished rust inhibitive action in addition to a high durability at elevated temperatures, but it contains a volatile rust inhibitor as one of rust inhibitor components, so a long term rust inhibition at elevated temperatures is not satisfactory, and as to the alkaline component such as magnesium oxide, etc., their influence on the environments must be taken into consideration.

A heat-resistant grease composition, which comprises fluoro-silicone oil, a fluororesin-based thickener, and an additive such as calcium alkylsulfonate, etc., and which can also contain other well known thickeners such as calcium stearate, etc. has been also proposed, where it is shown by evaporation tests or engine tests that the heat resistance is distinguished and also stable for a long time, but no mention is made of the rust inhibition, particularly even after having been subjected to heat resistance tests.

Patent Literature 2: JP-A-8-143883

The present applicant has previously proposed a lubricating grease composition, which comprises perfluoropolyether base oil, and a metal salt of aliphatic dicarboxylic acid as a thickener, where the applicant shows that the composition can further contain a powdery fluororesin to attain improvements of abrasion resistance of mating material, leakage resistance, detergency, etc.

Patent Literature 3: JP-A-2001-354986

It is recommended that in the proposed lubricating grease composition a mixing proportion of the metal salt of aliphatic dicarboxylic acid used as a thickener is about 1 to about 50% by weight, preferably 3 to 35% by weight, on the basis of the composition. In the disclosed Examples 1 to 14 relate to lubricating grease compositions consisting of two components, i.e. the thickener and perfluoropolyether oil, the thickener is used in such preferable mixing proportions.

As to the powdery fluororesin as an admixable component, it is recommended that the admixing proportion is not more than about 50% by weight, preferably about 3 to about 35% by weight, on the basis of the composition. In the disclosed Examples 15 to 17 relate to lubricating grease composition consisting of these three components, it is recommended that the admixing proportion of powdery fluororesin is 5% by weight, whereas that of metal salt of aliphatic dicarboxylic acid as a thickener is 15-25% by weight. As is known from such results, an increase in the admixing proportion of metal salt of aliphatic dicarboxylic acid as a thickener will inhibit any increase the admixing proportion of powdery fluororesin.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a lubricant composition with a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis, which comprises a fluoro-oil and an appropriate admixing proportion of powdery fluororesin as a thickener.

Means for Solving the Problem

The object of the present invention can be attained by a lubricant composition, which comprises a fluoro-oil, a powdery fluororesin thickener, and a Ca salt or a Na salt of aromatic sulfonic acid or saturated aliphatic dicarboxylic acid as a rust-inhibitive additive, where the proportion of the thickener is 10-40% by weight, and that of the additive is 0.3-10% by weight, on the basis of the total weight of the composition, the balance being the fluoro-oil. In general, perfluoropolyether oils are used as a fluoro-oil.

EFFECT OF THE INVENTION

The present lubricant composition has a distinguished rust inhibition, particularly even after having been subjected to heat hysteresis, and thus can be used widely in lubrication of machines and their parts to be used particularly outdoors, and specifically used in effective lubrication of bearings requiring substantial rust inhibition, heat resistance, low-temperature characteristics, load-carrying capacity, etc. in automobile auxiliary equipment such electric fan motors, fuel injector equipments, alternators, etc. of automobiles. Furthermore, the present lubricant composition can be used for lubrication of solid-solid contacts such as sliding parts of ball-and-roller bearings, slide bearings, sintered bearings, gears, valve, cocks, oil seals, rolls, electric contacts, etc.

BEST MODES FOR CARRYING OUT THE INVENTION

Fluoro-oil for use as a base oil generally includes perfluoropolyether oil. Perfluoropolyether represented by the following general formula can be used for this purpose:

RfO(CF₂O)_(x)(C₂F₄O)_(y)(C₃F₆O)_(z)Rf

Specifically, those represented, for example, by the following formulae (1)-(3) can be used, and in addition, the one represented by the following general formula (4) can be also used, where Rf is a perfluoro lower alkyl groups having 1-5 carbon atoms, preferably 1-3 carbon atoms, such as a perfluoromethyl group, a perfluoroethyl group, perfluoropropyl group, etc.

RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf  (1)

In the formula (1), m+n=3−200, and m:n=10−90:90−10, and the CF₂CF₂O group and the CF₂O group are in random combination in the main chain. The perfluoropolyether (1) can be obtained by complete fluorination of a precursor formed by photo-oxidation polymerization of tetra-fluoroethylene.

RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)(CF₂O)_(r)Rf  (2)

In the formula (2), p+q+r=3−200, q and r can be 0, respectively, and (q+r)/p=0-2:1, and the CF(CF₃)CF₂O group, the CF₂CF₂O group, and the CF₂O group are in random combination in the main chain. The perfluoropolyether (2) can be obtained by complete fluorination of a precursor formed by photo-oxidation polymerization of hexafluoropropene and tetra-fluoroethylene.

RfO[CF(CF₃)CF₂O]_(s)(CF₂CF₂O)_(t)Rf  (3)

In the formula (3), s+t=2-200, t can be 0, and t/s=0-2:1, and the CF(CF₃)CF₂O group and the CF₂CF₂O group are in random combination in the main chain, and the perfluoropolyether (3) can be obtained by complete fluorination of a precursor formed by photo-oxidation polymerization of hexafluoropropene and tetrafluoroethylene, or by anionic polymerization of hexafluoropropylene oxide or tetrafluoroethylene oxide in the presence of a cesium fluoride catalyst, followed by successive treatment of the resulting acid fluoride compound having a terminal-CF(CF₃)COF group with a fluorine gas.

F(CF₂CF₂CF₂O)₂₋₁₀₀C₂F₅  (4)

The perfluoropolyether (4) can be obtained by anionic polymerization of 2,2,3,3-tetrafluorooxetane in the presence of a cesium fluoride catalyst, followed by treatment of the resulting fluorine-containing polyether (CH₂CF₂CF₂O)_(n) under ultraviolet irradiation at about 160° to about 300° C. with a fluorine gas.

These perfluoropolyether base oils can be used alone or in a mixture thereof, and when used as a lubricating oil the viscosity (40° C.) is desirably about 5 to about 2,000 mm²/sec, preferably about 10 to about 1,500 mm²/sec. When the viscosity is less than about 5 mm²/sec., the evaporation rate will be increased, and will fail to satisfy the requirements for evaporation rate of 1.5% or less set forth in JIS ball-and-roller bearing grease, class 3 as a heat-resistant grease, whereas when the viscosity is more than about 2,000 mm²/sec, the pour point (JIS K-2283) will be more than 10° C., and bearings, gears, chains, etc. fail to start at low temperatures in the ordinary manner, resulting in necessary heating for starting, that is, a failure to meet the admissible limit to use as the ordinary grease.

Fluororesin for use herein as a thickener includes polytetrafluoroethylene [PTFE], tetrafluoroethylene-hexafluoropropene copolymer [FEP], perfluoroalkylene resin, etc., so far used as a lubricant. Polytetrafluoroethylene obtained by subjecting tetrafluoroethylene to such a process as emulsion polymerization, suspension polymerization, solution polymerization, or the like, thereby preparing polytetrafluoroethylene, followed by subjecting it to a treatment by such a process as heat decomposition, decomposition using electron beam irradiation, physical pulverization, or the like, thereby reducing the number average molecular weight Mn from about 1,000-1,000,000 to about 1,000-500,000, can be used. Tetrafluoroethylene-hexafluoropropene copolymer having a number average molecular weight of about 1,000 to about 600,000, obtained by conducting copolymerization reaction of tetrafluoroethylene and hexafluoropropene and treatment to reduce the molecular weight, in the same manner as in the case of polytetrafluoroethylene can be used. To obtain PTFE having a melting point of 300° C. or higher, which is suitable for use in the present invention, it is desirable that Mn is about 10,000 or more. Control of molecular weight can be also carried out by using a chain transfer agent during the copolymerization reaction. The resulting powdery fluororesin having, among others, an average primary particle size of generally about 500 μm, preferably about 0.1 to about 30 μm, can be used.

The powdery fluororesin can be used in a proportion of 10-40% by weight, preferably 15-35% by weight, on the basis of total weight with base oil and rust-inhibitive additive. When the fluororesin thickener is used in a proportion of above 40% by weight, the composition will be too hard, whereas in a proportion below 10% by weight, no satisfactory thickening capacity of fluororesin etc. can be obtained, resulting in deterioration such as oil separation, and any increase in scattering prevention and leakage prevention can be no more expected.

The powdery fluororesin can be used together with other thickeners, which include metal soaps such as Li soap, etc., urea resin, minerals such as bentonite, silica, clay, graphite, carbon, zinc oxide, etc., organic pigments, polyethylene, polypropylene, and polyamide. From the viewpoints of heat resistance and lubricability, it is preferable to use monoamide monocarboxylic acid metal salts, monoester carboxylic acid metal salts, diurea, triurea, tetraurea, etc. These other thickeners having a melting point of 300° C. or higher can be preferably used.

Aromatic sulfonic acid salts for use herein as a rust-inhibitive additive include, for example, Ca salts or Na salts of petroleum sulfonic acid, alkylbenzene sulfonic acid, dialkylnaphtharene sulfonic acid, etc. The sulfonic acid salts having an aromatic ring are distinguished in both heat resistance and rust inhibition.

Saturated aliphatic dicarboxylic acids, for use herein as a rust-inhibitive additive include, for example, Ca salts or Na salts of oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonamethylenedicarboxylic acid, decamethylenedicarboxylic acid, undecamethylenedicarboxylic acid, dodecamethylenedicarboxylic acid, tridecamethylnenedicarboxylic acid, tetradecamethylenedicarboxylic acid, pentadecamethylenedicarboxylic acid, hexadecamethylenedicarboxylic acid, heptadecamethylenedicarboxylic acid, octadecamethylenedicarboxylic acid, etc. These with an aliphatic group having 6-12 carbon atoms are preferably used particularly in respect to the distinguished rust inhibition.

These rust-inhibitive additives can be used in a proportion of 0.3-10% by weight, preferably 0.3-5% by weight, on the basis of total weight with base oil and powdery fluororesin thickener. In a proportion below 0.3% by weight no desired rust-inhibitive effect can be obtained, whereas in a proportion above 10% by weight no desired proportion of the thickener can be admixed, and no thickening effect can be expected.

Even among these aromatic sulfonic acids and saturated aliphatic dicarboxylic acids, the amine salts have no satisfactory heat resistance, whereas the Ba salts and Zn salts have satisfactory rust inhibition and heat resistance, but must be labeled from the viewpoint of recent environmental problem.

The lubricant composition can further contain other additives so far used in the conventional lubricant, such as an antioxidant, other rust-inhibitors, a corrosion inhibitor, an extreme pressure additive, an oiliness agent, a solid lubricant, etc., when required. The antioxidant includes, for example phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol, 4,4′-methylenebis(2,6-di-t-butylphenol), etc. and amine-based antioxidants such as alkyldiphenylamine, triphenylamine, phenyl-α-naphthylamine, phenothiazine, alkylated phenyl-α-naphtylamine, phenithiazine, alkylated phenithiazine, etc.

Other rust inhibitors include, for example, fatty acids, fatty acid amines, alkylsulfonic acid metal salts, alkylsulfonic acid amine salts, oxidiged paraffin, polyoxyalkylethers, etc. The corrosion inhibitors include, for example, benzotriazole, benzoimidazole, thiadiazole, etc.

The extreme pressure agent includes, for example, phospho-rus-based compounds such as phosphoric acid esters, phosphorous acid esters, phosphoric acid ester amine salts, etc., sulfur-based compounds such as sulfides, disulfides, etc., and sulfur-based compound metal salts, such as dialkyldithiophosphoric acid metal salts, dialkyldithiocarbamic acid metal salts, etc.

The oiliness agent includes, for example, fatty acids, or their esters, higher alcohols, polyhydric alcohols, or their esters, aliphatic amines, fatty acid monoglycerides, etc. The other solid lubricant includes, for example, molybdenum disulfide, graphite, boron nitride, silane nitride, etc.

The composition can be prepared by adding predetermined amounts of a powdery fluororesin thickener, a rust-inhibitive additive and other necessary additives to perfluoropolyether base oil, followed by through stirring in a stirring kettle, etc. and then by homogenization treatment through three-rolls, or in a high pressure homogenizer.

EXAMPLES

The present invention will be described below, referring to Examples.

Examples 1 to 25 and Comparative Examples 1 to 7

The following base oils, thickeners, and rust-inhibitive additives could be easily mixed together only by stirring, thereby preparing lubricant compositions.

[Base Oil]

A-1: RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf Viscosity (40° C.) 85 mm²/sec. A-2: RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf Viscosity (40° C.)150 mm²/sec. A-3: RfO[CF(CF₃)CF₂O]_(p)Rf Viscosity (40° C.)390 mm²/sec. A-4: RfO[CF(CF₃)CF₂O]_(p)(CF₂C)_(r)Rf Viscosity (40° C.)230 mm²/sec. A-5: F(CF₂CF₂CF₂O)₂₋₁₀₀C₂F₅ Viscosity (40° C.)200 mm²/sec.

[Thickener]

-   -   B-1: Emulsion-polymerized PTFE (molecular weight: 100−200×10³;         melting point: 330° C.; average primary particle size: 0.2 μm)     -   B-2: Suspension-polymerized PTFE (molecular weight: 10−100×10³;         melting point: 318° C.; average primary particle size: 5 μm)     -   B-3: Solution polymerized FEP (molecular weight: 50−150×10³;         melting point: 256° C.; average primary particle size: 0.2 μm)

[Rust-Inhibitive Additive]

-   -   C-1: Ca dinonylnaphthalene sulfonate     -   C-2: Na petroleum sulfonate     -   C-3: Na sebacate     -   C-4: PfO[CF(CF₃)CF₂O]_(n)CF(CF₃)COOH     -   C-5: Benzotriazole     -   C-6: Octylamine salt of dinonylnaphthalene sulfonic acid

The resulting lubricant compositions were subjected to MKO test (corrosion degree). The test included, in addition to the test under the following ordinary conditions, comparison of corrosion degrees after having been subjected to heat hysteresis at 180° C. for 500 hours as to heating grease-sealed test bearings, followed by similar test to the above.

<EKO Test (Corrosion Degree) According to DIN 51802>

1306K bearings were sealed with grease, amounted on an EKO tester, and tested under such cycle conditions as revolution rate: 80 rpm; revolution cycle: revolution for 8 hours→stoppage for 16 hours revolution for 8 hours stoppage for 16 hours revolution for 8 hours→stoppage for 108 hours (total 164 hours) to evaluate corrosion states on the outer race track surface of the bearing according to the following basis.

In the test, distilled water was used.

Corrosion

degree Appearance Evaluation basis 0 No corrosion No changes 1 Traces of Up to 3 corrosion points in sizes of 1 mm or corrosion less 2 Weakly Corroded portions at corrosion degree of 1 corroded or more being within 1% of the surface 3 Corroded Corrosion extended in a range of 1-5% of the surface 4 Strongly Corrosion extended in a range of 5-10% of corroded the surface 5 Much strong- Corrosion extended in a range of 10% or ly corroded more of the surface

The results are shown in the following Table together with components of the lubricant compositions.

TABLE EMK Test After Rust-inhibitive Normal heating Example Base oil Thickener additive corrosion corrosion No. Species wt. % Species wt. % Species wt. % degree degree Example 1 A-1 74.2 B-1 24 C-1 1.8 0 0 Example 2 ″ 74 ″ ″ C-2 2.0 0 1 Example 3 ″ 72.6 ″ ″ C-3 3.4 0 0 Example 4 ″ 67.2 B-2 31 C-1 1.8 0 0 Example 5 ″ 67 ″ ″ C-2 2.0 0 1 Example 6 ″ 65.6 ″ ″ C-3 3.4 0 0 Example 7 ″ 77.2 B-3 21 C-1 1.8 0 0 Example 8 ″ 77 ″ ″ C-2 2.0 0 1 Example 9 ″ 75.6 ″ ″ C-3 3.4 0 0 Example 10 A-2 74.2 B-1 24 C-1 1.8 0 0 Example 11 ″ 74 ″ ″ C-2 2.0 0 1 Example 12 ″ 72.6 ″ ″ C-3 3.4 0 0 Example 13 ″ 67.2 B-2 31 C-1 1.8 0 0 Example 14 ″ 67 ″ ″ C-2 2.0 0 1 Example 15 ″ 65.6 ″ ″ C-3 3.4 0 0 Example 16 A-3 74.2 B-1 24 C-1 1.8 0 0 Example 17 ″ 74 ″ ″ C-2 2.0 0 0 Example 18 ″ 67.2 B-2 31 C-1 1.8 0 0 Example 19 ″ 67 ″ ″ C-2 2.0 0 0 Example 20 A-4 74.2 B-1 24 C-1 1.8 0 0 Example 21 ″ 74 ″ ″ C-2 2.0 0 0 Example 22 ″ 72.6 ″ ″ C-3 3.4 0 0 Example 23 A-5 74.2 ″ ″ C-1 1.8 0 0 Example 24 ″ 74 ″ ″ C-2 2.0 0 0 Example 25 ″ 72.6 ″ ″ C-3 3.4 0 0 Comp. Ex. 1 A-1 73 ″ ″ C-4 3.0 4 5 Comp. Ex. 2 ″ 75 ″ ″ C-5 1.0 2 5 Comp. Ex. 3 ″ 74 ″ ″ C-6 2.0 0 5 Comp. Ex. 4 A-2 73 ″ ″ C-4 3.0 4 5 Comp. Ex. 5 ″ 75 ″ ″ C-5 1.0 2 5 Comp. Ex. 6 ″ 74 ″ ″ C-6 2.0 0 4 Comp. Ex. 7 A-1 61 ″ ″ C-3 15 — —

Lubricant composition of Comparative Example 7 had a consistency number (JIS K2220 7; corresponding to DIN ISO 2137) of No. 4 and therefore too hard impossible to test and to use as a practical grease. The lubricating oil composition of all the Examples had consistency numbers of Nos. 1-3, and could form greases successfully. 

1. A lubricant composition, which comprises a fluoro-oil, a powdery fluororesin thickener, and Ca salt or Na salt of aromatic sulfonic acid or saturated aliphatic dicarboxylic acid as a rust-inhibitive additive, where the thickener is in a proportion of 10-40% by weight, and the additive is in a proportion of 0.3-10% by weight on the basis of the total weight of the composition, the balance being the fluoro-oil.
 2. A lubricant composition according to claim 1, wherein the fluoro-oil is a perfluoropolyether, represented by the following general formula: (where Rf and Rf are the same of different perfluoroalkyl groups having 1-5 carbon atoms, x+y+z is 3-200, and x and y may be zero), or a perfluoropolyether, represented by the following general formula: F(CF₂CF₂CF₂O)_(n)C₂F₅  [II] (where n is an integer of 2-100)
 3. A lubricant composition according to claim 2, wherein the perfluoropolyether represented by the general formula [I] is at least one of perfluoropolyethers represented by the following general formulae: RfO(CF₂CF₂O)_(m)(CF₂O)_(n)Rf  (1) (where m+n=3-200, m:n=10−90:90−10, and the CF₂CF₂O group and the CF₂O group are in random combination in the main chain), RfO[CF(CF₃)CF₂O]_(p)(CF₂CF₂O)_(q)(CF₂O)_(r)Rf  (2) (where p+q+r=3-200, q and r may be zero, (g+r)/p=0−2, and the CF(CF₃)CF₂O group, the CF₂CF₂O group and the CF₂O group are in random combination in the main chain), and RfO[CF(CF₃)CF₂O](CF₂CF₂O)_(t)Rf  (3) (where s+t=3-200, t may be zero, t/s=0−2, and the CF(CF₃)CF₂O group and CF₂CF₂O group are in random combination in the maim chain)
 4. A lubricant composition according to claim 1, further comprising another thickener.
 5. A lubricant composition according to claim 2, further comprising another thickener.
 6. A lubricant composition according to claim 3, further comprising another thickener.
 7. A lubricant composition according to claim 1, for use as a grease.
 8. A lubricant composition according to claim 2, for use as a grease.
 9. A lubricant composition according to claim 3, for use as a grease. 